SU976507A1 - Method of non-destructive testing of bulk charge in dielectric materials - Google Patents

Description

one

The invention relates to a technique for measuring electrical charge in dielectric. They can also be used in electrical and electronic industries, as well as in research and production laboratories for non-destructive testing of internal electrostatic charges in dielectrics and the development of methods to combat their harmful effects.

There is a method of non-destructive control of volume charge, based on measuring the distribution of the field or potential in the bulk of the material and then calculating the distribution of the charge using the electrostatic formula 1.

However, this requires knowledge of the parameters of the dielectric, in particular the dielectric constant, which must be measured additionally. This makes it difficult to control the distribution of charge and reduces its accuracy.

Closest to the proposed method is a non-destructive testing of volumetric electric charge in dielectric materials by applying to the electrodes superimposed on the material under study an excitation signal and measuring the output signal characterizing the response of the material to the specified excitation 2.

However, this method does not provide high accuracy of control, since its implementation is also necessary

10 know the dielectric properties of the material under study, which cannot always be measured, and setting them by analogy gives significant errors in determining the charge.

15

The purpose of the invention is to increase the accuracy of the control.

This goal is achieved by the fact that according to the method of non-destructive testing

20 volumetric electric charge in dielectric materials by applying to the electrodes J superimposed on the material under study, an excitation signal

and measuring the output signal characterizing the response of the material to the specified excitation, use a voltage pulse between the electrodes as the excitation signal, creating in the study area a field strength of 10 - 10®-duration 1 (s, and as the output signal the deviation of the sections the surface of the material under study from an unperturbed state at different times.

FIG. 1 shows the time variation of the longitudinal wave sensor signal; in fig. 2 - change in time of the signal sensor transverse waves in a crystal Li F when exposed to a pulse of an electric field.

The method is based on the fact that the impact of an electric field pulse leads to the appearance in the material volume of a mechanical pulse, the magnitude and distribution of which unambiguously correspond to the magnitude and distribution of the volume charge in the sample. As a result, a traveling deformation wave is formed in the material, and a mechanical displacement occurs on the surface, the magnitude and measurement in time of which describe the charge distribution in the bulk of the material. The displacement on the surface of the test object can be converted into an electrical signal using piezo sensors placed on the sample surface. The registration of an electrical signal can be performed, for example, by oscillography.

The sensitivity of this method is determined by the size and duration of the applied external field pulse; the spatial resolution is determined by the pulse duration. Thus, the minimum pulse duration c is determined by the need for sufficient sensitivity, and the maximum - 10 s - by the requirement of sufficient spatial expansion for practically interesting specimen sizes (up to 2.5-1 O m) of various materials. The maximum value of the external field is determined by the voltage of the dielectric breakdown and does not exceed 10 V / m; minimum - 10 V / m should be sufficient to determine the charge distribution in larger specimens with the required resolution.

Example. The volumetric electric charge in the sample of alumoltrium rpaiiaTa in the form of a plate with thickness m is measured. The required spatial resolution is 1O m. The pulse amplitude of the external electric field is 1O V / m.

spatial resolution and equal to c. A crystal is used as the strain sensors. Under these conditions, the measurement sensitivity obtained is equal to C / m.

5 Example, p2. The sample of polymethacrylate has a thickness of 2.5-10 m. The spatial resolution is assumed to be 0.25-10 m. With this spatial resolution, the depth of the pulse is 10 s. When using a crystal receiving sensitivity of 10 C / m, the amplitude of the external electric field pulse is 10 V / m.

A feature of this method is that. when a pulse is applied during; The boogens in the sample generate both longitudinal and transverse deformation waves. Therefore, for their registration, tensile strain strain sensors and shear strain sensors can be used. Thus, it is possible to simultaneously record the distribution of electric charge along different directions in the sample.

Example 3: A LiF crystal is charged with a 1 MeV electron beam. To generate an external impulse of an electric field, a generator with a pulse duration of 3–3.3 s and an amplitude of 10 V is used, and a voltage of -10 V / m is created. To measure the acoustic

 The signal of the longitudinal wave sensor is located on the same surface as one of the excitation electrodes, the transverse wave sensor is located on the surface normal to the plane of the electrode. AT

0 as longitudinal wave sensor

Ui Mby crystal is used (2 cut), the transverse wave sensor is L.iNbOj (X cut). The velocity of the longitudinal waves in the material is 8-10 m / s (Fig. 1),

Claims (2)

5 transverse - 6-10 m / s (Fig. 2). The value of the sensor signal, equal to 10 V, corresponds to the density of the volume charge, equal to 10 C / m. The reliability of the results obtained by this method was checked by the methods of an acoustic probe and thermal CMD. All measurements for identical samples gave similar results. The observed minor discrepancies can be attributed to the possible heterogeneity of the dielectric properties of the materials, which are influenced by using the methods of an acoustic probe and a thermal one. Thus, the advantage of this method in comparison with the known ones is the possibility of direct measurement of volumetric electric charge and reduction of the influence of material properties on the measurement result, which increases the accuracy of control. Claims A method of nondestructively controlling bulk electrical charge in dielectric materials by applying an excitation signal to the electrodes superimposed on the material under investigation and measuring the output signal characterizing the response of the material to the specified excitation, characterized in influence of the properties of the material on the measurement result; a voltage pulse with inter-mentioned electrodes is used as the excitation signal, creating in the field of research dovani field strength of 10 + 1D + 1D -j5f duration with, and as an output signal - value deviations portions of the material surface from the undisturbed state at different times. Sources of information taken into account during the examination 1. To produce universities. Physics, 1974, No. 11, p. 99 2. USSR author's certificate for application No. 28774О1 / 18-21, cl. C 01 R 29/24, 1980 (prototype). Srig.